1. Field of the Invention
The invention relates to elongated, powered surgical instruments for use in endoscopic tissue resection. More particularly, the invention relates to an instrument having an elongated inner tube rotatably situated within an elongated stationary outer tube, both inner and outer tubes having, at their distal ends, cutting apertures which cooperate to resect or otherwise affect tissue during endoscopic surgical procedures. Still more particularly, the invention relates to the method of manufacturing the cutting aperture at the distal end of an elongated tubular member of a rotatable surgical instrument.
2. Description of the Prior Art
The use of elongated surgical cutting instruments has become well accepted in performing closed surgery such as arthroscopic or, more generally, endoscopic surgery. In closed surgery, access to the surgical site is gained via one or more portals, and instruments used in the surgical procedure must be elongated to permit the distal ends of the instruments to reach the surgical site. Surgical cutting instruments for use in closed surgery--also known as "shavers"--conventionally have a straight, elongated outer tubular member terminating at a distal end having an opening in the end or side wall (or both) to form a cutting port or window and a straight, elongated inner tubular member concentrically disposed in the outer tubular member and having a distal end disposed adjacent the opening in the distal end of the outer tubular member. The distal end of the inner tubular member has a surface or edge for engaging tissue via the opening in the outer tubular member and in many cases (but not all) cooperates with the opening to shear, cut or trim tissue. In some cases, such as burrs, the opening in the outer tube merely allows access to the tissue and does not otherwise cooperate to resect tissue. The inner tubular member is rotatably driven about its axis from its proximal end, normally via a handpiece having a small electric motor which is controlled by finger actuated switches on the handpiece, a foot switch or switches on a console supplying power to the handpiece. The distal end of the inner tubular member can have various configurations depending upon the surgical procedure to be performed, and the opening in the distal end of the outer tubular member has a configuration to cooperate with the particular configuration of the distal end of the inner tubular member. For example, the inner and outer tubular members can be configured to produce whisker cutting, synovial resection, arthroplasty burring or abrading, side cutting, meniscus cutting, trimming, full radius resection, end cutting and the like, and the various configurations are referred to generically as shaver blades. Cut tissue is aspirated through the hollow lumen of the inner tubular member to be collected via a vacuum tube communicating with the handpiece.
The aforementioned elongated surgical cutting instruments have also been produced in angled configurations in which the distal tips of the inner and outer members are aligned and offset or bent at either a fixed or variable angle from the proximal ends of the aligned inner and outer members. Examples of fixed and variable angle rotary surgical instruments are shown in U.S. Pat. Nos. 4,646,738 (Trott) and 5,411,514 (Fucci et al.), both assigned to the assignee hereof, and incorporated by reference herein. In other respects the operation of fixed and variable angle shavers is largely the same as that of the straight shavers described above.
One parameter affecting the efficiency of operation of shaver blades is sharpness of the edges of the windows. Various prior art designs are known to have differing degrees of sharpness of both the inner cutting edges and the periphery of the outer window. The present invention is concerned with the design and manufacture of an outer tubular member having a sharpened window periphery.
It is known that improved resection efficiency is achieved by sharpening the cutting edges and this is true of conventional scissors as well as endoscopic shavers although the manufacture of the latter is considerably more difficult. The smaller the included angle of the cutting edge, the sharper the edge. Clearly, below a certain limit the edge becomes too delicate to be practical. When applied to the tubular members of cylindrical, rotating shavers, the cutting edges on the inner member and the periphery of the outer window are the cooperating edges which should have the smallest included angles in order to produce sharp edges. However, this must be balanced with cost and speed of manufacture. In prior art designs, the outer window is sometimes formed by simply grinding or milling an opening at the distal tip of the outer tube, the opening lying in a plane angled relative to the tube axis. Thus, the outer window faces toward the end of the tube as well as toward the side. It will be understood that this process produces a generally elliptical window periphery which has a lower included angle at its proximal end and a larger included angle at its distal end. A land surface surrounds the periphery and is angled (in the cutting plane) such that the inner rim of the land defines the sharpened cutting edge of the outer member. The formation of this type of outer window could be achieved by a variety of two-dimensional through-cutting processes such as wire EDM (electrical discharge machining), ram EDM, conventional or electrochemical grinding or milling. For certain purposes, this type of cutting window may be sufficient, however, it is known that subjecting the land surface to additional processing can produce a sometimes more preferable "three-dimensional" window shape and sharper edge. The term "three-dimensional" is used to distinguish the opening from one formed by a simple planar cut through the tip of a tube: the periphery of the latter lies only in a two-dimensional plane while the periphery of the former also extends above and below this plane. However, the additional steps required to produce such sharpness entail the use of either a tool having a complex contour or a machining process capable of complex contouring motions (e.g., a computer numerical control (CNC) machine). Additionally, practical manufacture of these devices would be hampered because simultaneous production of several blades is more difficult with such processes, if at all possible.
It is accordingly an object of this invention to produce an outer member of a shaver blade assembly in which the window of the outer member has a sharpened periphery.
It is also an object of this invention to produce a shaver blade assembly having an outer member with a sharpened window formed by a peripheral land surface angled to the window rim.
It is another object of this invention to produce a sharpened outer window with a simple process minimizing the use of complex tools and the number of required processing steps.
It is yet another object of this invention to shape and sharpen a three-dimensional window in a tubular member of a rotatable surgical instrument with a single step process.